Enhance hold_lock_file_for_{update,append}() API

This changes the "die_on_error" boolean parameter to a mere "flags", and
changes the existing callers of hold_lock_file_for_update/append()
functions to pass LOCK_DIE_ON_ERROR.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-fetch-pack.c

@@ -813,7 +813,8 @@ struct ref *fetch_pack(struct fetch_pack_args *my_args,
 			  )
 			die("shallow file was changed during fetch");
 
-		fd = hold_lock_file_for_update(&lock, shallow, 1);
+		fd = hold_lock_file_for_update(&lock, shallow,
+					       LOCK_DIE_ON_ERROR);
 		if (!write_shallow_commits(fd, 0)) {
 			unlink(shallow);
 			rollback_lock_file(&lock);